Technology of Gold-, Silver-, and Copper Alloy Metalwork

Mag. Dr. Birgit Bühler

Light microscopic investigations on archaeological non-ferrous and precious metal objects are used for observation and photographic documentation of all technological features recognisable on the surface (e.g. tool marks, solder joints, granulation, filigree, niello) and therefor represent an important prerequisite for all further metallurgical investigations. The observed features are recorded for each object in a short description. In many cases, the result of the light microscopic investigations also serves as a decision-making aid as to whether further investigations (scanning electron microscopy, material analyses, microstructure investigations, experimental-archaeological methods) are necessary or sensible at this particular object and at which part of the object they are to be performed.

The observation of technological features, supplemented by the results of microstructural investigations, material analyses and experimental-archaeological methods, allows a reconstruction of the manufacturing process of individual objects and the formation of "technological" groups, which can be compared with the results of the archaeological evaluation. Particularly promising in this context seems to be a comparative examination of the tool marks, with particular attention to the fine tools (in particular piercers, chisels, different types of punches). For the linear decorating techniques, mainly three types of tools are used (piercers, chisels and punches). Piercers and chisels are «cutting tools», they have a sharp working edge, and metal is removed when they are used. The so resulting notch is V-shaped in its cross-section for both tool types, while "chipless machining" with a blunt-edged tool (e.g. a punch) merely deforms the metal and therefore leaves a rather U-shaped notch. Another basic distinguishing feature is whether the tool was guided by hand (mainly piercers) or with as driven forward with a hammer (chisels, punches). The latter can be recognised in most cases by numerous "breaks" running transversely to the longitudinal axis of the notch. On the other hand, engraved (i.e., carved) lines often show relatively fine scratches running parallel to the longitudinal axis. First, a detailed photographic documentation using the optical microscope, in some cases also on the scanning electron microscope is required. Scanning electron micrographs allow better detection and accurate measurement of tool marks. In addition to the recognition of different tool types, the identification of certain tools is possible on a case-by-case basis.

Ideally, the light microscopic examination of the surface can yield completely new insights into the production of a specific object. For example, when looking at the belt made of sheet gold dating to the Mid-Awarian Period from Igar-Vámszölöhegy (Find III) under the light microscope, the ornamentation of the overwhelming majority of the components shows individual tool marks, meaning that they where in no way - as originally suspected - produced using press plates.